Field of the Invention
The present disclosure relates to a liquid discharging head and a liquid discharging device that discharge a liquid such as ink.
Description of the Related Art
As a method of discharging a liquid from a liquid discharging head such as an inkjet recording head, a thermal inkjet method which adds heat to a liquid, which causes a film to boil, and which makes use of a bubbling force thereof is available. The liquid discharging head of a thermal inkjet type includes a recording element board that has a discharge port which discharges a liquid, a pressure chamber which communicates with the discharge port, a channel which supplies a liquid to the pressure chamber, and a supply port which supplies a liquid to the channel. A heating resistance element (heater) is formed in the pressure chamber, and the liquid is discharged from the discharge port by using discharge energy (heat) generated by the heating resistance element.
When the liquid is discharged by such a liquid discharging head, the discharged liquid is formed with a columnar shape including a main droplet and a long and narrow tail that is connected to and extends behind the main droplet. The tail frequently becomes a very small liquid droplet, called a satellite droplet, as a result of being separated from the main droplet by the surface tension of the liquid that is being ejected. When the satellite droplet lands on a location on a recording medium that is displaced from a location of the main droplet, the recording quality is reduced.
As a method of reducing the generation of such a satellite droplet, the specifications of Japanese Patent No. 4818276 and U.S. Patent Application Publication No. 2013/0021411 propose a method of forming a discharge port with a shape other than a circular shape. This corresponds to forming a region having high resistance and a region having low resistance in the discharge port with respect to discharge liquid droplets, and allows the generation of satellite droplets to be reduced by increasing the difference between the resistances of the two regions.
In a structure such as those described in the specifications of Japanese Patent No. 4818276 and U.S. Patent Application Publication No. 2013/0021411, when the liquid in the discharge port is evaporated and the viscosity of the liquid is increased or a solid component of the liquid adheres to the vicinity of the discharge port, in particular, the resistance of the region having high resistance is further increased, as a result of which it may be difficult to discharge the liquid. When it becomes difficult to discharge the liquid, a reduction in the speed of the liquid droplets or discharge failure occurs during discharge. Therefore, the liquid droplets no longer precisely land on a desired location of a recording medium, as a result of which a reduction in image quality occurs. Consequently, the resistance of the region having high resistance can only be increased to a certain resistance. Thus, there is a limit as to how effectively the generation of satellite droplets is reduced.